April Section 5. Basements

Transcription

1 April 2012 Section 5 Basements

2 Basements Basements Basement design Waterproofing BS 8102: 2009 Code of practice for protection of structures against water from the ground, gives three categories of waterproofing for a basement: Tanking A continuous waterproof barrier is applied to the inside or outside of the basement structure. Structurally integral protection Usually water resistant concrete in combination with a waterproof membrane Drained cavity Cavities are formed within the walls and floor to collect and drain away water entering the basement. Heat loss The pattern of heat loss from a basement wall is complex, with the rate of heat loss diminishing as the depth of the basement increases. This is due to the insulation value of the ground behind the basement wall. A method for calculating U-values for basements is given in BS EN ISO: Position of insulation Installing rigid insulation externally is the preferred method for insulating new basement walls. Key 1. Externally insulated External insulation is the preferred option for basements as the whole structure is kept warm, with negligible risk of condensation. The insulation should be placed up against the waterproofing membrane. Polyfoam ECO Floorboard (extruded polystyrene) is recommended because it has negligible moisture absorption and high compression resistance. A drainage membrane or layer of washed no fines gravel should be placed adjacent to the insulation. This relieves hydrostatic pressure and channels water to the foundation drain. The membrane or gravel should be covered with a geotextile to prevent fines from blocking the drainage material. 2. Internally insulated Internal insulation of basement walls is only recommended for existing basements where it is not possible to insulate the basement externally. New basements should be insulated externally. Any insulation system applied to the interior of the basement should have the following properties: It must allow the basement wall to dry out to the inside, for example by means of a cavity drainage system It must prevent warm moist air reaching the cold basement wall and condensing. A vapour control layer (vcl) should always be installed on the warm side of the insulation to prevent water vapour from the basement rooms condensing on the cold cavity drainage system. All joints, tears, overlaps and perforations in the vcl should be well sealed with an aluminised tape. Materials in contact with the basement wall and floor must be moisture tolerant, like, a closed cell extruded polystyrene board that is unaffected by moisture. The detail opposite shows a solution for an existing basement with solid brick walls, there is a drained cavity system directly behind the wall which drains to a sump. Other considerations The land around the building should slope away from the basement walls. Ideally the area adjacent to the building should have an impermeable finish, such as concrete paving. For new basements, a drain should be located around the perimeter of the basement and positioned at least 200mm below the finished level of the basement floor. It should be bedded and surrounded in free draining aggregate and wrapped in a geotextile before backfilling, to prevent fines from blocking the drain. Thermal insulation achievable by constructions within this document. Pb01 Find online. Visit knaufinsulation.co.uk and key in construction code to find the most up to date information on your chosen solution. Knauf Insulation solution U-values Wall insulated externally Product: Standard or Extra See page: 260 Ba01 Wall insulated internally Product: Standard or Extra See page: 262 Ba Technical Advice and Support Centre

3 Basements 1. Externally insulated basement walls Ground to slope away from wall and have impermeable finish wherever possible Basement and wall insulation to overlap Concrete block retaining wall with reinforced poured concrete infill Waterproofing membrane Cavity drainage membrane or use free-draining backfill below screed Geotextile membrane Perforated pipe as foundation drain, 200mm below basement floor, with coarse gravel surround 2. Internally insulated basement walls Continuity insulation with joints taped and sealant applied to junctions with surrounding structure Top of cavity drainage membrane sealed to prevent moisture escaping Plasterboard on timber or steel frame allows services to be installed Ground to slope away from wall and have impermeable finish wherever possible Existing basement wall Vapour control layer on the face of the insulation Cavity drainage membrane directs water from basement wall to sump in floor Technical Advice and Support Centre

4 Basements Basements Wall insulated externally Moisture resistant - long term exposure to water has a negligible impact on thermal performance Robust product, protects the waterproofing layer from damage High compressive strength, withstands the pressure exerted by the backfill Ba01 NEW BUILD Zero Ozone Depletion Potential (ODP) Global Warming Potential (GWP) <5 Geotextile membrane around drainage at base of wall Drainage channel membrane Basement wall Waterproof membrane Products s are rigid extruded polystyrene boards, they are lightweight, yet have excellent structural strength and long term effectiveness. Standard and Extra are suitable for the external insulation of basement walls. Typical construction Masonry or in-situ concrete basement walls (up to 2.5m deep) insulated with Polyfoam ECO Floorboard Standard placed against the tanking membrane. For basements between 2.5m and 5m deep, Extra is recommended for its greater compressive strength. The basement wall insulation is protected by a drainage cavity membrane which also reduces hydrostatic pressure and directs water to the foundation drain. Installation s are placed against the tanking membrane and protected by a drainage cavity membrane. Carefully backfill with free-draining granular material to hold the drainage cavity membrane and insulation in place. Where s project above the ground they should be covered by a reflective or light coloured flashing board, or similar, to prevent long term exposure of the insulation to Ultra Violet (UV) light. Performance Thermal insulation s have a thermal conductivity value of or W/mK, determined by thickness and product grade. 260 Technical Advice and Support Centre

5 Basements Junction of basement and external wall Cavity wall insulation Cavity tray Minimum 150mm overlap between wall and basement insulation to minimise thermal bridging Typical specification Install Standard*/ Extra*,...mm thick, against the tanking membrane. Cover with a drainage cavity membrane, manufactured by... and carefully backfill to hold the insulation in place. (*delete as appropriate) Alternatively, consult the National Building Specifications, Standard version clause/ clauses M21/210 Knauf Insulation specification clauses can be downloaded from knaufinsulation.co.uk/nbs Drainage channel membrane Reinforced concrete infill to engineer s design Waterproof membrane Compression resistance s are highly resistant to compression and are capable of withstanding both occasional and long term high static loads. Load bearing construction elements should be designed to adequately support the combination of imposed and dead loads without creating excessive deflection. Moisture resistance s have negligible water absorption and are unaffected by standing in ground water. Fire performance In the construction detailed above, Polyfoam ECO Floorboards are completely enclosed by other materials and will not contribute to the development stages of a fire or present a smoke or toxic hazard. Table 1 - Typical U-values for basement walls insulated externally Thickness (mm) U-values (W/m 2 K) for basement depth (m) of: Standard n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a Extra 75 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a Notes: The calculations assume that the basement floor has a U-value of 0.25 W/m 2 K. CERTIFICATE CS/ U Value Competency Scheme Technical Advice and Support Centre

6 Basements Basements Wall insulated internally Polyfoam Floorboard Versatile product, can be used to insulate both walls and floors High compressive strength accommodates the loads associated with the fit out of the basement Ba02 Vapour control layer Plasterboard Independent frame REFURB Robust and lightweight, making it easy to cut and handle on site Existing basement wall Polyfoam ECO Floorboard Standard BBA certified (floors) Zero Ozone Depletion Potential (ODP) Global Warming Potential (GWP) <5 Screed Slip layer Polyfoam ECO Floorboard Cavity drainage membrane Products Standard is a rigid extruded polystyrene board, it is lightweight, yet has excellent structural strength and long term effectiveness. Standard is suitable for the internal insulation of basement walls. Typical Construction Existing solid masonry basement wall with new cavity drainage membrane, Polyfoam ECO Floorboard Standard insulation and Knauf I stud independent lining. This system is most suitable for existing basement walls. The cavity drainage membrane collects any water that passes through the basement wall and drains it to a sump, from where it is pumped to a drain. The internal lining allows services to be accommodated. Installation Standard is fixed to the cavity drainage membrane using a nonsolvent based adhesive such as plaster adhesive. Ensure the floor and wall insulation are in intimate contact with each other and all joints fully closed. Install a vapour control layer on the warm side of the insulation. The vapour control layer should be free from holes and any gaps should be made good with tears repaired and overlaps sealed with aluminised tape. The wall vapour control layer should be sealed to the slip layer placed below the screed. After the floor slab or screed has been laid, construct the Knauf I stud lining and line the steel studwork with plasterboard. 262 Technical Advice and Support Centre

7 Basements Sump in basement floor Vapour control layer Discharge pipe to outside Inspection cover Sump pump Cavity drainage membrane drains into sump Typical specification Standard...mm thick, to be fixed directly against the drainage cavity membrane, with dabs of plaster adhesive. Tape all joints with an aluminium faced self-adhesive tape. Seal the junction between the Polyfoam ECO Floorboard Standard and the surrounding construction with a water resistant, solvent free silicone sealant. Alternatively, consult the National Building Specifications, Standard version clause/clauses M10/40 or M10/290 Knauf Insulation specification clauses can be downloaded from knaufinsulation.co.uk/nbs Performance Thermal performance Standard has a thermal conductivity value of or W/mK. Compression resistance Standard is highly resistant to compression and withstands both occasional and long term static loads. Load bearing construction elements should be designed to adequately support the combination of imposed and dead loads without creating excessive deflection. Table 2 - Typical U-values for basement walls insulated internally Thickness (mm) U-values (W/m 2 K) for basement depth (m) of: Standard Notes: The calculations assume that the basement floor has a U-value of 0.25 W/m 2 K. CERTIFICATE CS/ U Value Competency Scheme Moisture resistance Standard has negligible water absorption and is unaffected by standing in ground water. Fire performance In the construction shown above, Polyfoam ECO Floorboard Standard is completely enclosed by other materials and will not contribute to the development stages of a fire or present a smoke or toxic hazard. Table 3 - Compressive creep results for Polyfoam Floorboards Product Polyfoam ECO Floorboard Standard Load applied (kpa) Initial compression (%) Further compression after 50 years (%) Technical Advice and Support Centre

8 Disclaimer Knauf Insulation have a policy of continuous product development, therefore product information may change without notice. Wherever possible, products are manufactured to the appropriate British Standard (BS), or harmonised European Standards, (BS EN) and are supplied subject to our Terms and Conditions of Sale, a copy of which is available on request. Information within this book The designs and detailing shown in this publication are illustrative only, although every effort has been made to ensure the accuracy of all textual and pictorial content. Knauf Insulation, its employees and authorised agents can accept no liability whatsoever, either indirectly or directly arising from the use of its products in connection with any information or advice contained in this book. It is the responsibility of Designers, Clients and Installers to check that installations achieve the appropriate standard and comply with the relevant Building Regulations. The most up to date British or European standards should be referenced at all times. Knauf Insulation Ltd PO Box 10 Stafford Road St Helens Merseyside WA10 3NS Tel: info.uk@knaufinsulation.com Ref: GB Knauf Insulation Ltd Customer Service (Sales) Technical Advice and Support Centre Literature PO Box 10 Tel: Tel: Tel: Stafford Road Fax: Fax: Fax: St Helens sales.uk@knaufinsulation.com technical.uk@knaufinsulation.com info.uk@knaufinsulation.com Merseyside WA10 3NS